RESEARCH UPDATE: WATER TREATMENT RESIDUALS

As most people are aware, drinking water is treated before distribution to users. Coagulation and flocculation are the processes by which various materials are removed from drinking water, and water treatment residuals (WTR) are the byproduct. Water treatment facilities previously could dispose of WTR in surface waters, but this is no longer permitted. With increasing restrictions on landfills, there is a need to identify alternative uses for WTR.

Because WTR is similar in many ways to a finely textured soil, proposed uses include that of a soil substitute, particularly in land-reclamation projects. To help determine the suitability of WTR for this, researchers at Oklahoma State University examined the ability of WTR from three water treatment facilities to support plant growth. Bermudagrass was used in the study because this grass is frequently planted in reclamation projects.

The researchers noted that the main problem with WTR is phosphorus (P) deficiency in plants. High levels of aluminum and iron oxides present in WTR are apparently to blame. Adding P to the WTR did not improve plant uptake, the researchers found.

Though P deficiency may limit WTR's utility where optimum growing conditions are required, situations where sub-optimal growth is acceptable — such as land reclamation projects — might allow WTR to be an adequate soil substitute. The researchers found that two of the three WTRs supported growth of bermudagrass to a degree adequate for reclamation projects.

The third WTR exhibited P availability too low for adequate growth. However, the researchers suggested an interesting alternate use for WTRs that won't support growth. The low P availability of some WTR is due to high sorption. That is, it binds nutrients tightly. That may make it an excellent “sink” when incorporated into agricultural soils with high P levels. This might reduce P runoff from high-phosphorus soils.